In accordance with U.S. Pat. No. 5,401,457 for PROCESS FOR FORMING A COLOR COATED ARTICLE, By Emery I. Valyi, Patented Mar. 28, 1995, a process is provided for forming a color coated article. In accordance with the ""457 patent, a film is placed substantially flat over a mold cavity and deformed by a core mold half and by molten plastic entering through a sprue.
An alternate method consists of thermoforming the film to nest accurately in the mold cavity, with said operation being carried out independently of the mold. The formed film insert is then brought to the mold and placed into the cavity. This procedure is described by Ch. Fridley, Avery Dennison, in Product Finishing, Apr. 19, 1992, and European Patent 0,442,128 to Beyer, and other publications. The Avery procedure entails a forming process of the film that is well known and widely practiced for other uses. It is a low pressure process for shaping the film or sheet, in solid condition, at relatively low temperatures. This holds for all of the several variants of thermoforming, such as vacuum forming, whether the vacuum is to suck the film into the cavity, or onto the core, as well as thermoforming followed by a sizing operation.
The result of this is a product whose dimensional accuracy and shape conformance is not within the range of a high pressure forming process, such as injection molding or compression molding. Consequently, the thermoformed preform, while nesting in the mold cavity or slipped over the core, fails to conform to them fully. Thus, upon injecting or compressing plastic behind the preform, the preform will deform producing localized surface imperfections. These imperfections may be dimensionally insignificant but optically discernible and therefore may provide a product of insufficient quality for an automotive finish, for example. In addition, the cost of a separately made film insert is relatively high, considerable trim scrap is generated, and the handling (transport, destacking, insertion) become expensive.
The procedure of the ""457 patent overcomes the above defects; however, it is difficult to control, particularly when molding parts with large surfaces and sharply varying curvature. The difficulties increase when the plastic is pressure molded at high enough temperatures to reduce the film strength substantially, as in the case of conventional injection molding.
In applying either of the above processes to large, panel-like structures, it was found, moreover, that the procedure of injection molding of the ""457 patent and Avery Dennison procedure referred to above, is difficult to carry out, requiring extremely costly equipment, and prone to produce imperfections at the interface between the film layer and the injected plastic.
Accordingly, it is a principal object of the present invention to provide a process and apparatus which conveniently and expeditiously forms a molded article from molten plastic and a film insert, wherein the film is the outer layer of the molded article and wherein desirably the film is colored.
It is a further object of the present invention to provide a process and apparatus as aforesaid which overcomes the foregoing defects and provides a commercially feasible process and apparatus for forming a color coated article.
It is a still further object of the present invention to provide a process and apparatus as aforesaid which is operative under conditions that are sufficiently controllable and cost efficient to produce complex parts, particularly those of a size of major body components of passenger cars.
Further objects and advantages of the present invention will appear hereinbelow.
In accordance with the present invention, the foregoing objects and advantages are readily obtained.
The present invention includes a process for preparing a molded article, which comprises: providing a mold cavity; placing a film or blank over the mold cavity; depositing molten plastic on said film to form a combination of a film with molten plastic thereon; and subsequently forming said film-molten plastic combination in said mold cavity into a molded article having the shape of said mold cavity, wherein the film is an outer layer of the molded article. Desirably, the film is colored and is held over the mold cavity and molten plastic is deposited onto the film. Also, preferably the combination is formed into the shape of the mold cavity at least in part by a mold core which compresses the combination and forms the combination into the shape of the mold cavity. Thus, the resultant article is desirably a molded, color coated article having a desired shape, which may be a complex shape, as defined by the shape of mold cavity. Naturally, the mold may include other components, such as slides and lifters which are well known.
The present invention also includes an apparatus for preparing a molded plastic article, which comprises: a mold cavity; means for holding a film or blank, desirably a colored film, over the mold cavity; means for depositing molten plastic onto said film to form a combination of a film with molten plastic thereon; and means for forming said film-molten plastic combination subsequent to depositing molten plastic onto said film in said mold cavity into a molded article having the shape of the mold cavity, wherein the film is an outer layer of the molded article.
The present invention adheres to the principle of forming the film in uniformity with the plastic that backs same, and thereby to effect full shape conformance without optically discernable flaws of the exposed film surface, which may be a paint film, and to form the resultant molded article under closely controlled conditions of temperature distribution and pressure in an efficient manner.
Further specific features and advantages of the present invention will appear hereinbelow.